Electron beam recording apparatus



Sept. 26, 1961 1.. E. WALKUP ELECTRON BEAM RECORDING APPARATUS FiledJuly 15, 1958 5 Sheets-Sheet 1 T-R SWITCH TRANSMITTER TIMER HORIZONTALSWEEP RECEIVER GATE RECORDER INVENTOR. Lewis E.Walkup F/Gl BY M Ma W ATTORNE Y Sept. 26, 1961 E. WALKUP ELECTRON BEAM RECORDING APPARATUSFiled July 15, 1958 5 Sheets-Sheet 2 FIG. 2

INVENTOR. Lewis E. Walkup Sept. 26, 1961 L.. E. WALKUP ELECTRON BEAMRECORDING APPARATUS Filed July 15, 1958 5 Sheets-Sheet 3 50-, PICKUP WEBas- PICKUP WEB 25-,L PICKUP WEB [IO-p. PICKUP WEB ZERO PICKUP WEBTHICKNESS C c c w w w o o 0 m 6 6 4 2 20 60 Air Gap, ,4.

INVENTOR. Lewis E.Walkup ATTORNEY L. E. WALKUP 5 Sheets-Sheet 5 ELECTRONBEAM RECORDING APPARATUS Sept. 26, 1961 Filed July 15, 1958 DEVELOPMENTv35 MECHANISM I 1 I I II," I]

-5a (F) '1 & FUsER BY flu W77 INVENTOR. Lewis E.Walkup United StatesPatent 3,001,848 a r ELECTRON BEAM RECORDING. APPARATUS Lewis E. Walkup,Columbus, Ohio, assiguor, by mesne assignments, to Xerox Corporation, acorporation of New York J t Filed July 15, 1958, Ser. No. 748,655 '2Claims. (Cl. 34674) by electrical transmission wherein the imageintelligence is carried in the form of.varying characteristics of 'electrical transmission denotative of the intelligence. At the recordingstation suitable means are provided for transducing the electricaltransmission into a visual form and reducing the same to record,permanent or transitory as the needs dictate. In many environments thesensing of the intelligence to be transmitted and the transmissionthereof, particularly when sensed electronically or optically, may beeffected with extreme rapidity. However, the transducing and reductionof the intelligence to visual and record form frequently imposes serioustime limitations on the overall system due to the inability of therecording station to accept the information at the rate capabilities ofthe sensing and transmission systems.

Electron beam or cathode ray tubes with phosphor screens, due to theirability to respond essentially instantaneously to electricalintelligence applied thereto, have therefore commonly been resorted toas a means for transducing the electricallyfltransmitted intelligenceinto visual forms. However, the image on the phosphor screens of suchtubes is transitorygand doesnot of itself afford a suitable means fordisplaying a-large amount '1 of intelligence simultaneously, or amemoryof intel ligence for any significant period of time, particularly if thenature of the transmitted intelligence is continuous- 'ly varying.Numerous efiorts have been directed to recording permanently thetransitory images from cathode ray tubes by various optical photographicmethods. For many purposes such optical photographic recording is notwell adapted, because of the time delay between ex} posure anddeveloping of the record, the need for'wet 3,391,848 Patented Sept. 26,1961 i More particularly, in accordance with the present invention, anelectron beam is caused to repetitively traverse a single line of scanat a desired repetition rate. The target scanned by this beam is formedbasically from a block of material highly resistive electrically andsubstantially opaque to (i.e. essentially non-transmissive of) p theimpinging electron beam. Embedded within the target along the line ofscan is a row of electrically conducting pins, each isolatedelectrically from the others by the target material. With each traverseof the target, the beam deposits an electron charge on the pins. The

, quantity of charge deposited on each pin may be caused tovary inaccordance with variations in the beam current during the traverse, asrequired by electrical intell gence signals fed to the recordingstation. While one side of the target is thus repetitively traversed bythe electron beam, a web of dielectric sheet material is fed past and inclose proximity to the opposite side of the target. Maintaining one sideof the web grounded orat a suitable potential difierence from thetarget, the air dielectric between the target and web is disrupted andionized, resulting in the positive ions traveling to the target, and thenegative ions traveling to the web and establishing a correspondingcharge thereon. If the web is properly positioned relative to thetarget, the resultant charge thus induced on the web will constitute aline of charge, and the quantity of charge along the length of the linewill correspond to the quantity of charge and variations thereof created.on the line of pins in the target by the electron beam. Thus, for eachtraverse of the target by the electron beam, a line of electrostaticcharge is-induced on the web corresponding to the intelligence fed tothe recording station. The rate of move-.

developing techniques and equipment, and the sensitivity of optical filmto cosmic, nuclear, and other radiation; The foregoing drawbacksofoptical photographic recording systems are particularly apparent inthe environment of military radar, where the equipment may be installedin high altitude reconnaissance craft, and where the need responsecharacteristics of such beams. However, rather than utilizing a phosphorscreen to convert the intelligence to visual form with the foregoingattendant limitations thereof and disadvantages in the ensuing opticalphotographic recording of the phosphor image, in accordance with thepresent invention, the beam is utilized to create an electrostatic imageon a moving web, and by xerographic techniques, the electrostatic imagemay be immediately and continuously developed into a visual image, and,if desired, formed into a permanent record. I P

, means and methods.

ment of the web past the target, and the rate of scan of the target bythe electron beam are appropriately correlated to provide on the web asuccession of lines of electrostatic charge which taken together denotethe image or facsimile intelligence fed to the recording station. Thiselectrostatic image may be continuously developed by xerognaphic meansto provide a visual image of the intelligence, and this image may, ifdesired, be fixed to a permanent record. It is accordingly one object ofthe present invention to provide for the recording of intelligencepresented in electrical form. a 7

Another object of the present invention is to provide for the recordingof facsimile or image intelligence.

, A further object of the present invention is to provide for therecording of intelligence presented in electrical form and transduced torecord form by use of an electron 'beam.

A still further object of the present invention is to provide for. thereduction of intelligence carried as a modulation of an electron beaminto record form.

, .-An additional object of the present invention is to provide for thereduction of intelligence carried as a modulation of an electron beaminto record form by Xerographic Other objects and advantages of thepresent invention will become apparent to those skilled in the art froma consideration of the following detailed description of one exemplaryspecific embodiment of the present invention had in conjunction With theaccompanying drawings,

wherein:

FIG. 1 is an exemplary presentation ofone embodiment or the presentinvention, showing a radar system in functional block diagramcooperating with an electron beam recorder illustrated schematically;

FIG. 2 is an enlarged detailed view, partially in section, oftheelectron beam target used in FIG. 1 and the adjacent image receivingweb;

accuses Xerographic developing system used in conjunction with theelectron beam recorder of the present invention.

As previously indicated, one environment in which it contemplated thatthe present invention will find important utility is that of recordingintelligence derived from a radar scanning system. So far as the Presentinvention is concerned, the particular radar system, or the particularmode of radar scan, is not material. However, in FIG, 1 there ispresented schematically an exemplary embodiment of a recorder embodyingthe princi'plesof the present invention, in conjunction with afunctional block diagram of ageneralized radar system.

h r r e .10 is ShDWH wi hin a dfl hfid ,face 48 and forreasonssubsequently explained is bent line box being fed intelligencefrom a radar system. The radar system comprises a transmitter 11,feeding an antenna 12. The reflected energy received by the antenna istransmitted through the T-R switch 13 to receiver '14, Whose detectedoutput is fed to the recorder through a gating circuit 15. Timer 16keyed by the radar transmissions triggers a horizontal sweep circuit '17for the recorder and the gating circuit to program and synchronize thehorizontal sweep sequence of the recorder with the application of thereceived radar intelligence. The radar received intelligence andhorizontal sweep output are applied from circuits 15 and 17 to the rescorder 10. The recorder comprises a cathode ray tube 21, whose electrongun and beam control circuits are of conventional design. These includea 'cathodeZ-Z, control grid 23, first and second anodes 24 and 25,electrostatic horizontal deflection plates 26, electrostaticverticaldeflection plates 27, and intensifying ring 28, all operated in aconventional manner from a suitable power supply generally indicated as29. The output of the radar receiver 14 as passed by the gating circuit15 is appliedto the control grid of the electron gun, and'thus controlsthe electron beam current. The output of the horizontal sweep circuit 17is applied across the horizontalbeam d e-. flection plates 26, and thuscontrols the electron beam scan pattern and sequence across the targetof 'the cathode'ra'y tube. It may be mentioned at this time that thevertieal beam deflection plates 27 are adjustably set to aselected biasvalue. The reason-for-thisig as will become'apparent subsequently, thatthe present'recorder operates "on 'only onehorizontal'line or verticalposition for the electron beam. a

Considering the general operationof the apparatus thus far described,for each scan cycle of the-radar'system, the reflected energy denotingthat scan cycle 'is passed by the gate 15 and applied to the controlgrid 23 of the-electron gun in tube 2.1. Simultaneously and intimed'relation thereto, the electron beam is caused to effect-one scanacross the tube target, generally denoted by numeral 31 in tube face 46,the vertical deflection plates of the tube being biased-to this verticalbeam angle. The intelligence contained in the reflected radar energy,which may for example be in thetime of receiving the'reflected energyorin the intensity thereof, or both, is utilized to modulate the currentin the electron beam of tube 21 through-operation of the control grid23,, Thus, as determined by the radar intelligence, a varying quantityof charge, or a'varye ing charge pattern, is established along thehorizontal scan line of the target 31 for each scan cycle of the electron beam. As will be more fully explained subsequently, from thischarge pattern applied to the target 31, acon responding line of chargepattern is induced on that portion of the web '32 immediately adjacentthe target, Thus, as each successive line of intelligence, so to'speak,is ob tained from-the radar system, it is accordinglytransducedontosuccessive lines of the web 32 as the latter is advanced past thetarget from supply roll 33 to take-up roll 84.

At 35 the electrostatic charge pattern thus induced on web 32 isdeveloped by usual xerographic means into a visual image, therebyproviding a visual facsimile presentation and record of the information,such as the topography, scanned by the radar system.

The electron beam target per se 31 is shown in FIG'. 3 g as arectangular block of material havinga high electria cal resistance, andwhich is substantially impervious to the electrons impinged thereon bythe electron beam. The

target may be formed, for example, from polymethyl methaerylate orglass, or otherhigh resistance material.

having a resistivity of at least 10 ohm-cm. Embedded within the targetmaterial .31' is a line of pins 44, each extending transversely throughthe target arid lying in the plane 40 indicated in dotted lines.

I The pins are formed from a conducting material such as tungsten wire.

- One end of each pin 44 is formed flush with the surfac cathode ray tueam esi d by arrows 41 imp 4-7 of target 3.1, while the other endextendsfrom the sin of the current to the pins, with the result that thepins will become positively charged rather than negatively charged.Certain compounds, generally suitably activated oxides suchcesiumozrygen-silver compounds, produce electron yields of from 4m 6. Toobtain an effective charge multiplication in the pins utilizing thiseffect as by coating the portions of the pins receiving the primaryelectron beam witha cesium-oxygen-silver compound) req nros the controlof a number of factorssuch as relatively low primary electronpotentials, the angle of incidense of the primary electrons to'thetarget surface, etc.

As .shQWn in FIG. 2, the target 31 is sealed in the face of cathode mytube 21, with the flush ends of pins 44 on the exterior of the tube, andthe bent ends, or tails,"45 on the interior of the tube. Electrons fromthe ta ls 45 a d a e t collected. on t ep 4: Immediately opposite andexterior of the target 3-1 there isypo ned a mandrel 43 or electricalconducting material whf h may be grounded .as shown, or have a positivepotential applied thereto. Web 52 0t dielectric material, such aspolyethylene terephthalate aluminized on the surface contacting mandrel43, is passedover the tip offltlhe mandrel 43 in intimate electricalcontact there- W1 ,he electron charges accumulated on the pins 44 set upelectrostatic'fields between the pins and the mandrel 43, and-when thepotentials of these fields are of suficient magnitude, the air in thespace 49 between pins 44 and Web 132 s on ze The p sitive ion aattracted to he pins, while the negative ions are attracted to the web.

spot on-web 3g-is a functionof the charge present on that 7 Pinimmediate y opposite he sp on e 32 1 co sideration: S am the-ch r p e to any pa tiw a ri ie d func io ct e c beam cu n mp n d thereon, and thisin turn is a function of the radar intellin s ob aine from h ra a s miti app re t a o ea h-cycle o c along target 31by beam e t f i e lisen einduc d acro s t e eb. it he a ation o in igenc Within t a i e b i dened by e va i ti n harge i du e th rec I As pre i us men oned, the p n 44a e p ide th depen in ta ls 45.: Th purpo e of the tails is to eliminatetheinced for critical :adjustmentof the vertical deflec+ tionanglejotiztheeleetronheam, since the beam may aimpinge r-nponianyportion:of -theteils rather than be required to be precisely-adjustedtothe'line of the pins.

The foregoing description of the present invention sets where E is thepin potential with respect to ground in volts, Q is accumulated chargeon the pin in coulombs, and C is the pin-capacitance to ground infarads.

Since 7 where C; is the capacitance of the area of the pickup sheetadjacent to the pin, in farads, and.

C is the capacitance of the pin to the pickup sheet in farads;

therefore,

This potential, E, from pin to ground consists of two components, one, Eis across the air gap from the pin' to the surface of the pickup sheet,and the second is across the pickup web. E can be expressed as:

where E is the potential across the gap in volts.

The potential across the Whole system can therefore be expressed as;

If E is the breakdown potential of air for the air gap thicknessused,.then E is that potential which, when applied to the pin, will justinitiate electrical breakdown in the air gap and, hence, cause chargeinduction on the present invention because of poor image qualitygenerally produced. 7

FIG. 6 presents a graph of image width as a function of pin potentialand air gap distance for three air gap distances, 6n, l2,u., and 25p,using pins having a diameter of 25 Upper and lower limits of'themeasured image widths are presented, as well as the range common to allthree air gaps. The values given are those obtained with the mandrel andpickup web adjusted to optimum obtainable-lateralalignment with the lineof pins in the tube. From this graph one may observe that a resolutionof 10 lines/ mm. is obtainable, and such is considered an importantminimum limitation upon good quality facsimile reproduction. Image widthincreases with increasing pin potential. Image width appears to beindependent of air gap in the ranges of 6 1. to 25 11.. For gaps greaterthan 25 however, image width increases rapidpickup web in response, topin potential; Thus, this potential: always will be greater than thatnecessary to break down the air gap alone, and assuming no electricalleakage, will depend on the capacitance of the pins and the pickup web.Equation 5 is approximate, in that spreading of the electric field isneglected. However, experimental results have shown this equation to bequite accurate. Based on Equation 5, FIG. 4 shows graphically therelationship of air gap distance 49* to pin potential required forcharge induction on the pickup web, for various thicknesses ofpolyethylene terephthalate Webs. As a generalization from said graph, itshould be noted that for each thickness of pickup web there is a minimumvalue of charge induction potentialoccurring in the air gap range offrom about 10 1. to about 30 In FIG. 5 there is presented theexperimentally ascertained relationship of minimum pin potential to airgap for obtaining an induced xerographically developable.

charge on a pickup web of polyethylene terephthalate having athicknessof 35;. It may be observed from this graph that air gaps in the range offrom 6 to 25 require a pinpotential of from about 600 volts to 800volts. These ranges represent the preferred operating ranges of thepresentinvention. It has been found that air gaps greater-than 5011. areunsuitable for the purposes of the ly' with increased air gap.

The matter of lateral alignment of the mandrel and pickup web with therow of pins in the tube is mentioned above. The tolerance with respectto this parameter has been found to be about p at an air gap of 6p,increasing to a maximum of 200g with a 12;/. air gap, and decreasingagain to about 100p. with an air gap of 25 1.. By tolerance herein ismeant the lateral range over which image induction is had on the web atthe minimum transfer potential as shownin FIG. 5. Although the greatesttolerance in lateral positioning is had with an air gap of about 12 itis preferred to utilize a 25 air gap, which would be less diflicult tomaintain than 12 and accept the reduced tolerance in lateral alignment.

Accordingly, it may be summarized that to render the invention hereindescribed suitable for facsimile recording, the following operationalcharacteristics must be met: The air gap between pins and pickup webmust be less than 50g, and preferably between 6,14 and 25 1. The pinpotential must be at least in the range of from about 600 volts at a 6air gap to about 900 volts at a 50p. air gap, when using a pickup webhaving the capacitance of 35 1. thick polyethylene terephthalate(polyethylene terephthalate has a dielectric constant of approximately3.5), the voltages generally increasing with increasing air gap, and offrom about 600 volts to about 800 volts in the preferred air gap rangeof 6p. to 25 For maximum line resolution, the pin potential should bekept close to the minimum value at which xerographically developablecharge induction occurs.

It has been shown that with tungsten pins of 25p. in diameter spacedfrom each other 50 $0 125, on centers, embedded in a polymethylmethacrylate block, line resolution of better than 10 lines/mm. isobtainable, if the foregoing parameters are adhered to. Of course, theelectron beam scanning the target must have a diameter at the target ofless than the line resolution sought. Electron beam guns arecommercially available with beam diameters substantially less than ,0.1mm. In order to obtain the pin potentials required, the electron beamgun should also be capable of an acceleration potential of 5 to 10 kv.,and an electron beam current of 1 ampere. These requirements togetherwith a beam spot of less than 0.1 mm. are available in a Type 5Felectron gun.

With reference to FIGS. 7 and 8, there is presented the principles of,and an exemplary mechanism for, transforming into visual form theelectrostatic image of intelligence induced on web 32 by operation ofthe electron beam. The thin electrically insulating web 3 2 drawn fromsupply roll 33 may be a plastic film, such as polyethyleneterephthalate, polystyrene, cellulose acetate, ethyl cellulose, or likesheet material of good insulating properties, and preferably 'of theorder of one or two mils thick; or it may be of paper coated on theworking surface with one of theseplastics, or with a wax; or in someinstances thoroughly dry paper or cellophane. can be used,v As theweb 32is drawn from its roll 33, it first passes through a preliminarycharging device 51, where the web is broughtto a uniform state .ofelectrostatic charge. From the preliminary charger, the web is thenpassed between'the electron beam target of tube 21 adjacentfone surfaceof the web, and the ground mandrel 43 adjacent the opposite surface,where'an electrostatic charge pattern depicting the intelligence isinduced on the web. The web then enters a development mechanism 35,where the electrostatic charge pattern on the web is rendered w'sible bythe selective application of a finely di-' vided-material, such aselectroscopic powder, 'or a liquid ink, or like material. As the webemerges from the developer, the intelligence carried thereon is visuallyintelligibleQ Where 'a permanent record of .the intelligence j isde'sire'd, the web i'sthen passed to fuse'r 57, where the powder isIpermanently fused to the web, "or the ink is dried. As is apparent, ifonly a transitory presentation of the intelligence is desired, the fusermay be omitted,-

and instead of a fresh web supply roll, the web may be in the form of anendless belt, with means interposed between .the developer 35 and thepreliminary charger 51,

on the return side, to clean the intelligence off the web.

potentiometer 55 is center-tapped to ground, and the battery 'ofvoltagesource53 is preferably one hundred to several hundred volts. By varyingthe potentiometer setting, one can thus establish afield of eitherpolarity and of adjustable intensity betweenelectrode 52 and web 32 Thealpha or other ionizing particles emitted by the radioactive layer onelectrode 52 produce ionization of the air in the chamber 51 intonegative and positive ions, and these ions migrate in oppositedirections, depending on their polarity, under the influence of theelectrostatic field existing between electrode 52 and plate 54. As ionsof one polarity deposit their charge on web 32, the field becomesaltered by the charge on the web until a state of equilibrium i reached,in which the potential of the web surface is equal to the potentialapplied to electrode 52 by the potentiometer. Whether a small positivepotential' or negative potential is applied to the web, as controlled bythe setting of the potentiometer tap, depends on factorssubsequently'considered. In some instances the electrode 52 may be heldat ground potential, in which case the device merely serves to removeincidentally acquired electrostatic charges from the web in preparationfor receiving the electrostatic intelligence charge pattern. Instead ofa radioactive source of ionizing particles, the electrostatic chargesmay be supplied by corona emission as disclosed, for example, in U.S.2,777,957 to L. E.

Walkup. With the web 32 thus prepared, it is passed be-' tween theelectron beam target of tube 21 and mandrel 43 19 receive theintelligence "charge pattern, as aforedescr'ibed. The web 32'carryingthe intelligence in electrostatic charge form, passes fromintelligence'transducing station into the developer 35, shownschematically in FIG. :5. This device comprises a pair of rollers 60 and65. 'Roller6tl includes alcentral bearing shaft '64 carrying a pair ofaxially spaced disks 62 over which the web edge peripheries pass.Flanges 61 confinethe web in place on disks 62. The web and disks 62thus form a hopper in which a supply of electroscopic powder 63 iscontained. It is preferable, although not necessary, that the powder 63be "charged by triboelectric or other means to carry an "electrostaticcharge opposite from that induced on the web at the transducing station.The p'owderadheres in jtlie charged areas to produce avisiblepresentation of the intelligence carried by thewe b. As thepowder is tumbled over theweb 32, if the initial preliminary charging ofthe web at 51 were of apolarity opposite from t at obtained at the tube21, then this background charge on th'eweb'would be of the same polarityas the charged powder, and would assist in repelling the developer:powder from this background area. After being developed, the Web passesfrom roller 60 up over roller 65,;and down into fuser 57. In'fuser 57,the web passesabout roller 58 where it, is heated to a temperaturesuflici'ent-to fuse the developer powder to the web, or, if ink wereused as the developer, to dry the ink thereon, thus form; ing apermanent visual and directly readable record of the intelligencetransduced at tube 21. The web may then pass between suitable driverolls such as 8i).

The described method of rendering the pattern of electrostatic chargesvisible, i.e., developing the image, is known as loop development. This'syst'ein' isdisclosed in U.S. Patent 2,761,416 to C. F. "Carlson; Themethod of development is not critical in the 'inst'ahtinvention andother methods for contacting electrostatica-lly charged markingparticles with the electrostatic image may be used. Thus a spray ofelectrostatically charged liquid droplets or dry powder particles, asdisclosed in 1 U.S. Patent 2,784,109 to L. E. Walkup may be used ormagnetic brush development described in U.S. Patent 2,791,949 to Simmonsand .Saul are all operable. -A powder cloud development apparatusparticularly 'suited for use as developer 35 in the present system isthe ,de-

vice known as.a slot development apparatus'mo'r'e p'articularlydescribed in U.S. 2,815,734 to C. F; Carlson. --Dejvices such as thatdescribed in' said U.S. 2,815,734 have been made wherein the developmentsystem is limited to A inchythereby making possible almost instantaneousviewing of the developed image. The choice of apartic'ular developingprocess or apparatus would obviously be=dependent on the combinationanddesign limitations imposed in assembling the machine for a particularoperation.

Similarly, the means of permanently afiixing the powder image to thebacking material is not critical in the instant invention. Thus, if nopermanent image is de: sired, after examination of the roll, the looselyadhering powder image may be wiped oif as by swabbing with cotton or arapidly rotating fur brush and the roll reused.

If a permanent record is desired, the powder particles may be renderedadherent to the backing material by heating, as previously disclosedherein, by contacting the powderbearing sheet with the vapors of asolvent for'the marking particles or for a resin coating on the imagereceiving member as disclosed for example in U.S. Patent 2,776,907 to C.F. Carlson. Where liquid droplets are used, absorption of the liquidinto the capillaries of the backing-mermber or an evaporation of theliquid would serve to 'afiix the imageto the image receiving sheet.Other means of aflixing the powder image, as by the use of pressure, byspraying with a fixative'liquid, etc.,' also may be used if desired. Ifdesired the image may be transferred from dielectric web 32 to an imagesupport member as paper and affixed thereto with web 32 being recycledin the image-forming process. 7

The possibility of using a pin tube for direct electron beam recordinghas long been obvious to those skilled in the art. Heretofore, however,it has not been possible to obtain dependable operation with highresolution. Thus this manner while using the instant invention 10-15lines 7 per mm. are easily obtained) it has also been suggested -tospace the-image receiving web from the pins, hut-under conditions ofvoltage and spacing causing poor-resolution or undependable operation,or both, Theinstant -invention for the first time presents the criticalinterrelationship between potential and spacing required for highresolution and dependable operation.

From the foregoing detailed exemplary description of the presentinvention, it will be appreciated that there is presented a method andmeans for recording electrically transmitted intelligence, utilizing anelectron beam as the means of transducing the electrical form ofintelligence onto record form, in such manner as the record may berendered visual and permanent, if desired, by usual xerographictechniques. Although the present recording technique has beenillustrated in conjunction with a radar system for sensing andpresenting the intelligence to be recorded, such is presented only asexemplary of one field of use for the present invention. As will beapparent to those skilled in the art, the present invention maybe'utilized generally in the field of recording, and it is not intendedthat the foregoing description shall be interpreted as limiting thescope of the present invention to radar. Also, other variations,modifications and adaptations of the present invention will be apparentto those skilled in the art, and such as come Within the spirit andscope of the appended claims are considered to be embraced by thepresent invention.

I claim:

1. A cathode ray device comprising an envelope, an electron gun in saidenvelope for projecting a beam of electrons, and a target in the face ofsaid envelope to which said beam is directed, said target comprising ablock of material essentially non-transmissive of electrons impingedthereon by said beam and having a high electrical resistance, aplurality of electrically conducting pins embedded in said blockextending through said block from the interior of said envelope to theexterior thereof and arranged in a line, the ends of said pins extendingto the interior of said envelope having portions extending exten'orly ofsaid block and angularly disposed relative to the portions thereofembedded in said block, said angularly disposed portions beingsubstantially parallel to each other, whereby said electron beam mayscan said pins by traversing said angularly disposed portions, means tomodulate said electron beam and an electrically conductive mandreladjacent said pins but spaced therefrom and adapted to support a web ofelectrically insulat- ,ing material in spaced parallel relation to saidpins at a distance of from about 6 to about 50 microns, said mandrelbeing in electrical circuit with said gun whereby a charge establishedon said pins by scanning thereof by said beam will disrupt the airbetween said pins and web and thereby induce an electrostatic charge onsaid web in accordance with the electron charge carried by said pins.

2. A device as set forth in claim 1 wherein said electron beam ismodulated by varying the current thereof.

References Cited in the file of this patent UNITED STATES PATENTS2,273,793 Ekstrand Feb. 17, 1942 2,283,148 Bruce May 12, 1942 2,657,377Gray Oct. 27, 1953 2,829,025 Clemens Apr. 11, 1958 FOREIGN PATENTS1,077,037 France Nov. 3, 1954

